The proposed investigations are an extension of past and current NIH supported studies which are directed toward seeking a broad understanding of all the circumstances and events relating to the act of blood-feeding in mosquitoes. Continued emphasis will be placed on mosquitoes which are known or suspected vectors of disease and major pest species. Established serological methods will be used to further characterize the natural feeding patterns of less common but potentially important species and new methods will be applied to give more specific data on the avian, rabbit, and rodent hosts of certain species incriminated as enzootic vectors of EE, SLE, CE, and VE in Florida. The natural incidence of multiple feeding and its relation to host- interrupted feeding will be explored to gain new insight on this aspect of feeding behavior and its potential for amplifying transmission. The feeding patterns of mosquitoes (as established by blood-meal identifications on field material) will be further investigated in large screened enclosures where the availability, number, location, and type of hosts (as well as mosquitoes and the semi-natural environment) can be manipulated at will. The attractiveness of different hosts will be compared using immobilized individuals. The importance of the various physical and behavioral characteristics of both mosquitoes and hosts in the development of mosquito-host relationships will be explored. Instances of fixed host preference (innate specificity) which are revealed by these studies will be confirmed and partially defined through arena studies of host-seeking behavior in the field and under laboratory conditions by wind-tunnel olfactometry.